Fix Cyton impedance check board configuration

[philippitts]

The Cyton impedance check configuration appears to be incorrectly disconnecting SRB2 and using Bias instead. This has led to incorrect impedance measurements as shown in https://github.com/OpenBCI/OpenBCI_GUI/issues/1204. This fix results in correct measurements with a 51 kOhm resistor - more tests to follow.

[philippitts]

Resistor Value	Pin	GUI Impedance Reading
51 kOhm	SRB2	50 kOhm
51 kOhm	1P	50 kOhm

Resistor Value	Pin	GUI Impedance Reading
470 kOhm	SRB2	550 kOhm
470 kOhm	1P	553 kOhm

Resistor Value	Pin	GUI Impedance Reading
680 kOhm	SRB2	649 kOhm
680 kOhm	1P	647 kOhm

Resistor Value	Pin	GUI Impedance Reading
1000 kOhm	SRB2	906 kOhm
1000 kOhm	1P	902 kOhm

[retiutut]

It looks like the macOS build pipeline is broken, which is not related to the code that was pushed.

I'd like to replicate these results using resistors as part of the review. The code is fine.

Great work @philippitts !

[wjcroft]

Forum users have been reporting broken impedance function well before March 2024. I would estimate many months. Totally appreciate Philip tracking this down.

On the Forum thread below I have suggested that users who need a workaround can try building the GUI from source using Phil's 2 line fix.

https://openbci.com/forum/index.php?p=/discussion/3790/high-impedance#latest https://openbci.com/forum/index.php?p=/discussion/comment/20284/#Comment_20284

Until the new GUI app download binaries are regenerated, you can apply the fix yourself using the GUI source code.

https://github.com/OpenBCI/OpenBCI_GUI/pull/1211 https://github.com/OpenBCI/OpenBCI_GUI/pull/1211/commits/b3918c8814e1d7869e0c9430812724671bfda3ec https://github.com/OpenBCI/OpenBCI_GUI/issues/1204#issuecomment-1970392296

Currently most staff are busy on the Galea project, several important demos at conferences are happening this week. Once things settle back to normal, new download binaries should be available.

https://docs.openbci.com/Software/OpenBCISoftware/GUIDocs/#running-the-openbci-gui-from-the-processing-ide

On the other hand, MANY groups using Cyton for university research projects, depend on accurate impedance checks to comply with their academic research protocols. So a wider distribution of this repaired GUI would be welcome.

@jartuso also commented recently on Slack: "this is the cyton impedance problem that we've talked about before. @philippitts didn't we fix this? This one scares me." What you may want to be concerned about is that universities getting wind of this in larger numbers, could dampen sales.

[isaacplotkin]

I just validated Phil's results. Looks good to merge @retiutut

[isaacplotkin]

Resistor Value	Pin	GUI Impedance Reading
1000 kOhm	SRB2	966 kOhm
1000 kOhm	1P	955 kOhm

Resistor Value	Pin	GUI Impedance Reading
100 kOhm	SRB2	100 kOhm
100 kOhm	1P	100 kOhm